Protective helmets for outdoor activities such as cycling are generally hemispherical in shape, conforming approximately to the shape of the top of the head, and are made of rigid, thick, impact absorbing materials designed to protect the head from being damaged if the user falls against a hard surface, including a protrusion such as a kerb stone, or if hit by a falling object such as may be encountered on a building site, quarry or mine. There are a specific rigorous safety standards required for different sporting activities. Helmets which meet these standards are typically bulky and awkward to store or put in a bag etc when not being worn.